1. Field of the Invention
The present invention relates to an apparatus for determining the sensitometric characteristics of a photographic emulsion. The emulsion to be tested may be in its fluid state or it may be a solid or semi-solid disposed on a substrate.
2. Background Art
The commercial production of photographic film involves the preparation of very large batches, on the order of 1500 L, of chemically complex photographic emulsions whose batch-to-batch variation in photographic response must be kept to a minimum. The photographic characteristics of an emulsion (contrast, speed, reciprocity, maximum density and fog) are commonly referred to as its sensitometric properties. Currently sensitometric properties are assayed on each batch of emulsion by actually running a portion of the emulsion through the commercial scale coating machinery to provide a section of coated web, exposing the emulsion in a controlled fashion in a sensitometer, developing the image by conventional processing bath technology, and measuring the image in a densitometer. This assay method is very time-consuming, wastes large amounts of materials, yields data slowly and is almost completely inflexible to changing parameters.
An example of an apparatus that coats and cures an emulsion on a scale that can be used for testing is given in U.S. Pat. No. 4,415,610 (Choinski) which discloses a coating system incorporating a chilling zone simulator and a drying zone simulator. The coating system is preferably adapted to coat relatively short lengths of web, and to be cleaned and recharged rapidly with different compositions for coating another short section of web. Means are provided for stopping a coated length of web in the chill zone simulator. The chilled web is then rapidly advanced into a drying zone simulator, where the web is again stopped. After the desired sequence of drying cycles is completed, the dried web is rapidly advanced to a sampling section in which a relatively short section of dried coated web may be cut off for testing.
The art provides several examples of apparatus that can be used to assess various sensitometric properties of emulsions when the emulsion is supplied already coated on a web. In some cases the developing process is carried out separately, and in others the developing process is carried out on commercial scale equipment that offers virtually no provision for modulating temperature or process chemistry in response to changing emulsions.
U.S. Pat. No. 4,365,895 (Shaber et al.) discloses an apparatus for evaluating an X-ray film processor. The disclosure specifically relates to a densitometer and the circuitry and logic necessary for the densitometer to provide information which can be used by an operator to assess the operational status of a film processor. There is no teaching with regard to developing or transporting the material being tested from an exposure location to densitometer.
U S. Pat. No. 4,464,036 (Taniguchi et al.) discloses an apparatus for controlling the activity of a photographic developing solution. A difference is obtained between a standard optical density and a test optical density, both measured at a certain point in a developing process. The difference is used to drive a corrective action: either adding an appropriate amount of supplementary solution or putting an exposed film into the developing solution.
U.S. Pat. No. 4,527,878 (Taniguchi et al.) discloses an apparatus very similar to that in U.S. Pat. No. 4,464,036 for an analogous correction in developing baths.
U.S. Pat. No. 3,995,959 (Shaber) discloses a densitometer coupled to a logic circuit the output of which produces a diagnostic indication of whether the chemistry of the film processor from which the test strip was derived is within acceptable limits. The only transport of the test substrate is a calibrated movement through the densitometer.
U.S. Pat. No. 4,611,918 (Nishida et al.) discloses a method for determining the optimum exposure conditions for a photographic color printer. The method is performed by preparing a plurality of test prints under different exposure conditions using a standard negative film, measuring optical density for each of the color components on the test prints, comparing their optical density with that of the corresponding color component on a standard print, detecting a change in optical density per unit positional change of correction key on each of the test prints with respect to each of the color components, and determining corrective value required for correcting the density difference between each of test prints and a standard print with reference to the change in optical density per unit positional change of correction key. The test procedure is illustrated as integrated into a standard color printer which has a developing section and a drying section through which the print is moved. The developing and drying time are modulated in a fixed ratio by the speed of transport of the paper. The chemistry of the developing bath is determined by the composition with which the bath is filled at the start of processing.
U.S. Pat. No. 4,128,325 (Melander et al.) discloses an automatic calibration system for use in a replenishment system for a processor of photosensitive material. The invention includes a sensing means which senses when photosensitive material approaches a density sensor. When photosensitive material is sensed approaching the density sensor, a calibration means monitors the signal from the density sensor and provides a calibration signal which automatically calibrates the density sensor. This calibration is performed before the photosensitive material reaches the density sensor.
U.S. Pat. No. 4,985,320 (Griffin) discloses a method and apparatus for controlling replenishment chemistry in a photographic film processor. It includes a calibration circuit using a light source and a photodetector and having one or more predetermined density values located on a reference control strip, the location thereof being used for comparative purposes with the location of equivalent density value on a developer test control strip. The quantified difference between the measured and reference location is used to control automatically the film replenishment chemistry.
None of the references discloses a system wherein the developing conditions can be modified in a programmable fashion so that the sensitometric properties of the various emulsions can be evaluated. The art addresses itself to systems for evaluating and, in some cases, adjusting large scale processes for developing film or prints. (Throughout the application the term "develop" will be used in place of the more technically accepted term "process" when confusion can be avoided thereby.) In all cases where the evaluation apparatus is a part of an apparatus for processing a photosensitive material, the developing process is carried out in a standard bath or baths through which the photosensitive material is drawn. In such a system, changing the parameters of the developing process in response to a change in the fundamental chemistry of a different photographic emulsion may require many hours, often a whole work day. The bath must be emptied, cleaned and refilled with a large volume of often expensive chemicals; the temperature must be equilibrated; the path length or speed of transport must be modified. If the developing process requires sequential exposure to multiple processing chemicals, the problem increases geometrically. There thus exists a need for an apparatus which can evaluate test batches of differing photographic emulsions on a web by exposing them, processing them and measuring their sensitivity in a practical time frame.
Photographic emulsions are prepared commercially in large batches. While the chemical characteristics of a batch can be monitored on an aliquot of the batch, there has heretofore been no convenient way to assay the sensitometric properties of a small aliquot of emulsion. There is thus a need for an apparatus that can coat a web with an aliquot of an emulsion, cure the emulsion, and then evaluate the sensitivity of the emulsion.